The free agent starting pitching market is headlined by guys like Dallas Keuchel, Patrick Corbin, and J.A. Happ this offseason, but there are other intriguing names who are likely heavily available on the trade market as well. Those two individuals consist of Robbie Ray of the Arizona Diamondbacks and James Paxton of the Seattle Mariners.

As is the case in the free agent starting pitching market, both pitchers are lefties and would immediately boost any teams starting rotation depth or plans down the stretch heading into and including the postseason. Of course, with that demand and the fact that both Ray and Paxton are lefties, comes a hefty price tag and one that both the Diamondbacks and Mariners likely would demand before a trade was officially agreed upon.

However, assuming that a team offers what it takes to pry one or both lefties away from their respective teams, the question becomes: which lefty would you rather have in your starting rotation? Anytime you are trying to evaluate two different pitchers or position players, there are always going to be certain things that favor one over the other, which is the case in this situation.

Regardless, let's dig into the data and try to answer the question as best as we can. The data integrated in this article is the data that every front office across the league will use in their evaluations and pursuit of either Robbie Ray and/or James Paxton as well as the usual eye test.

From an ERA perspective, things seem to favor James Paxton by almost as much as a half a run. Of course, it doesn't seem like a big deal, but sometimes the potential for that extra run to score can be a big deal for certain teams depending on the situation as well as how many runners are on base. From a workload perspective, Ray has thrown a little more than 40 innings compared to Paxton, over the past three seasons. Regardless, each starter has averaged at least 135 innings each of the last three seasons, which has to be taken into consideration. Both have had health problems, but it's not like they missed a substantial amount of time or couldn't give the Diamondbacks or Mariners - 18 to 20 starts - every year.

As a side note, teams are trending in the direction of analyzing another new analytical stat known as, Skill-Interactive Earned Run Average, or SIERA. With this new metric, it strives to understand the actual skill level of any pitcher being evaluated and determine if their overall ERA was right on target or if it should have been higher or lower than what it actually was. In the case of Robbie Ray and James Paxton, Paxton had the lower SIERA value at (3.39), while Ray had a SIERA value of (3.65), the past three seasons.

Strikeouts Per 9 (2016-2018)

Robbie Ray: 11.76 K/9James Paxton: 10.37 K/9

This category is a big one because it's both starting pitchers selling points to perspective teams. Both Robbie Ray and James Paxton have developed the reputation of being strikeout lefties during their big league tenure, to this point, but Robbie Ray has a considerable advantage over James Paxton when it comes to throwing strikes. As indicated, Ray has averaged at least one more strikeout over Paxton during each of the starts that he has made, over the span of the last three seasons.

Walks Per 9 (2016-2018)

Robbie Ray: 4.15 BB/9James Paxton: 2.22 BB/9

Out of all of the categories that will be discussed in this article, this is probably the one that separates Robbie Ray and James Paxton the most. Over his big league career, there have been situations where Robbie Ray has had trouble commanding the strike zone, thus allowing a walk to the opposing teams batters and losing out in situations where he can strike out the batter especially with runners on base. In all, James Paxton has allowed close to 2 walks less than Robbie Ray has over the past three seasons, which definitely has to be taken into consideration.

Home Runs Per 9 (2016-2018)

Robbie Ray: 1.29 HR/9James Paxton: 0.88 HR/9

Again, there isn't a huge disparity in this category between the amount of home runs that James Paxton has allowed compared to Robbie Ray the last three seasons, but it does favor Paxton because he has allowed less than 1 home run-per-9 innings, which can be a big deal. From a league wide standpoint, that puts Paxton 106th among qualified starting pitchers, while Robbie Ray ranks near the top of the list (32nd), tied with the likes of Julio Teheran, Jamie Garcia, and Jerad Eickhoff.

Left On-Base Percentage (2016-2018)

Robbie Ray: 76.7%James Paxton: 72.5%

Overall, this category probably doesn't weigh too heavily into the evaluation process for inquiring teams about either Robbie Ray or James Paxton, but it's still important to point out. In the bigger picture, Robbie Ray has been more successful the past three seasons in those high leverage situations, where there might be runners on base with two outs, compared to James Paxton. Granted, a pitcher's left on-base percentage is always going to be skewed based on the defense behind the pitcher and the catcher calling the pitch, but it can somewhat play into how effective a pitcher is during certain situations that might arise during a regular season or postseason game.

Groundball-to-Flyball Percentage (2016-2018)

Robbie Ray: 1.16 GB/FBJames Paxton: 1.27 GB/FB

Over the past three seasons, both Robbie Ray and James Paxton have been nearly identical in regard to their groundball-to-flyball ratio or percentage. Both pitchers have done well in that regard and are basically middle of the pack, among qualified starters, in this category. Of course, between Chase Field and the Mariners old stadium, Safeco Field which has since been renamed, Chase Field has been more of a flyball ballpark. That's one reason why Robbie Ray seemed to have moments of brilliance over the past three seasons with the Diamondbacks.

Here is another category that more and more teams seem to be placing an emphasis on during their evaluation process for pitchers. With this category, it is split as there is no one clear individual who wins both categories between Ray and Paxton. Overall, Paxton has been more successful with getting hitters to swing for outs over the course of the past three seasons, but has allowed more contact compared to Ray over that span. For Robbie Ray, the lower swing percentage could play a significant role in why his walks-per-9 rate is so much higher than Paxton's. If the bases are loaded and there are two outs in an inning, Ray is more likely to walk in a run than Paxton, who would stand a higher chance of striking out the hitter at the plate.

One final category that's also important to take note of is the pitch type for, both starters and relievers, something that is taken into account when teams are making their evaluations or plans for how they plan to potentially use an acquired pitcher. You can't necessarily make a total evaluation of how effective a starting pitcher might be based on the types of pitches that they throw, but when you are a General Manager, it's important to take it into consideration because you want to have a balanced pitching staff and rotation, that has pitchers that can throw a variety of pitches. Of course, it is going to depend on the home ballpark and how effective one pitch might be versus another, but that's an entirely different topic for conversation in another article.

The point of posting the statistics for the past three seasons, showing the different percentages on the five main pitches for both Robbie Ray and James Paxton, was to simply showcase the difference in percentages. Robbie Ray relies heavily on his slider (20.1% of the time as indicated above), but does not have a cutter like James Paxton does, who relies on it (13.4%) of the time. Beyond that startling difference, both pitchers are somewhat alike in terms of the pitch types they offer to perspective teams.